Complex electronic devices are commonly formed on substrates through the deposition and patterning of multiple layers of conductive, semiconductive, and dielectric materials so as to form multiple individual electronic components. For example, large area imager arrays (e.g., having an area of about 200 square centimeters or more) are commonly fabricated on a wafer and contain photodiodes and circuitry for reading the output of the photodiodes, such as address lines and switching components (e.g., thin film transistors). Defects in such imager arrays can result from, among other causes, impurities in materials deposited to form the various components. One example of such an impurity-based defect is an unwanted conductive path, or short circuit, between two conductive layers separated by a dielectric layer. Such defects can disrupt the desired electrical connections between devices in the array and thus seriously degrade the performance of one or more of the individual electronic components on the wafer, often to the point of making an entire wafer unusable. It is thus advantageous to be able to repair defects in a wafer, either during the fabrication process, or after completion of the wafer.
Repair schemes for wafers often involve having different making connections to backup address lines incorporated into the wafer, such as is disclosed in U.S. Pat. No. 4,688,896 of Castleberry, U.S. Pat. No. 4,840,459 of Strong, and U.S. Pat. No. 5,062,690 of Whetten, all of which are assigned to the assignee of the present invention. This type of approach is primarily useful in repairing shorts between components, such as address lines, that are substantially disposed horizontally with respect to the other in the array; this approach is less feasible to use when the defect is a short circuit between a large conductive layer, such as the transparent common electrode disposed over the photosensor array, and an underlying component, such as an address line or photodiode pixel, separated by a substantially transparent dielectric material. In particular, such a "vertical" defect (i.e., short circuit or conductive path between the two layers, disposed one over the other and separated by a dielectric layer) can occur almost anywhere in the large area covered by the common electrode. Further, lasers of the type used in address line repair necessarily are powerful enough to penetrate deep into the array and thus typically are too powerful to use to ablate only a portion of the common electrode, which commonly comprises a transparent conducting oxide (TCO), layer, without damaging the underlying electronic component. Laser techniques for repair of individual address lines further require precise alignment so as to sever only the correct portion of one address line disposed closely to other components and address lines.
It is thus an object of this invention to provide a method of repairing an electronic-array structure having an undesired conductive path between two layers of electronic components in the array such that the situs of the conductive path can be isolated in one layer of the electronic components without causing damage to the other electronic component layer.
It is a further object of this invention to provide a method to selectively ablate a portion of the a conductive layer without completely removing a dielectric layer disposed thereunder.
It is still a further object of this array to provide a facile method of repairing a photosensor array having a TCO layer disposed thereover by electrically isolating the portion of the TCO layer at which the vertical short exists without breaking the electrical integrity of underlying components of the imager array.